Posted: 9/19/2011 11:11:47 AM EDT
| I want to be able to run a small fridge and a couple of lights [3 or 4 tops]. what do I need. |
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A small fridge use more energy than larger (for volume), I recommend a bigger unit. You need to identify how much power your fridge and lights use and how long you'll use them. Convert to KW/hrs.
Then it's all math (taking into account location - NY is like a 3.5-4 hours of sunshine, loss for charging of batteries, loss in AC conversion). If you can see the startup load and running loads, that will size your battery array and inverter. |
Wow how about speaking in normal terms
I just want like 2 12 volt lights inside my little 12x24 cabin, and to be able to keep stuff cold in a fridge but I'm a dummy. I know the panels go on the roof wired to some box then to the lights and I guess thru an inverter to be able to plug the fridge in right. How many watts does a smaller residential fridge need say one of those 18 cu. Ft ones |
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Quoted:
Wow how about speaking in normal terms
I just want like 2 12 volt lights inside my little 12x24 cabin, and to be able to keep stuff cold in a fridge but I'm a dummy. I know the panels go on the roof wired to some box then to the lights and I guess thru an inverter to be able to plug the fridge in right. How many watts does a smaller residential fridge need say one of those 18 cu. Ft ones Sorry... your 12v lights, how many watts? I'd guess <30W total (maybe CFL 13W equivs). Nothing much there. figure you'd want to run your lights 8 hours a day = 8x30W=240W/hrs The fridge depends if it is new (energystar) or old. A new fridge uses 311KW/hr per year (or 850W/hr in a day). But that is average across a year. In summer, figure 20-30% more usage (and converse in winter). So peak, in summer might be 1105W/hr in a day. So a total load of 1350W/hr in a day. Given you don't want to pull more than 50% of your battery capacity, that means you need at least 2700W/hr in battery capacity. Include 10% wiring/inverter loss, so you want 3000W/hr in battery. Assuming your cabin doesn't freeze/swelter (which affects battery capacity, life, and charing) your cheapest long term battery would be golf carts 6v batteries. 3000W/hr / /6v = 500A/hr. So if you get 150A/hr batteries, you'd need 4 (giving you 4x150x6=3600W/hr). Now, depending on where you are in NY, you get 3.5 to 4 hours of usable PV time. Take your 1350W/hr divide by 3.5 hours = 385W/hr needed from your PV array. I figure 10% loss for charge controller efficiency (a good controller can get to 96+% theoretical efficiency). Depending on if you want to account for the normal loss due to age of the panels (can be 10-15% at 20 years).. 385+ 10% for charger loss= 423W. You'd need that much in capacity of panels (more if you want to cover aging of panels, or if you want to have more capacity due to overcast or winter usage[less direct light and also less time]. Obviously, when you say cabin, it can't be deep in a forest. You need to make sure you mount the panels with the right orientation and azimuth. For optimal performance tracking or adjustable mounts (to change for summer/winter orientation - +7-10% gains). Anyway, hope that helps. There are lots of variables. I didn't figure total startup loading (as I assume you'll run this continuously, so the initial start draw (2x running, needs to be well within the inverter load, the battery discharge capacity, and even the capacity of your BIG thick battery-to-inverter cables). |
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This should clear up your question...
http://www.ar15.com/forums/t_10_17/638662_Solve_an_EMERGENCY_REFRIGERATION__problem_and_get_an_almost_complete_electrical_system_FREE.html |